On most mass market lines daytime is casual & you will see everything, even things you woudl prefer not to have seen
Smart casual is fine. Think of it this way, if you can wear it on a golf course (other than the short) or to the O-Club on post, you should be fine. Some lines do prefer men to have collared shirts so a T-shirt probably won't cut it but a golf shirt or a Hawian shirt will be fine. he doesn't always have to have a jacket on; I "make" my guy throw one over whatever he's wearing so I can sneak things into the pockets or steal it when the AC gets to me.